I have a CollectionView with 3 Cells which extend across the whole device's screen and basically represent my 3 main views.
I have paging enabled, so it basically works exactly like the iOS home screen right now.
My problem is that I want the "default" position of this CollectionView to be equal to view.frame.width so that the second Cell is the "default" view and I can swipe left and right to get to my secondary views.
I have already tried via
collectionView.scrollToItem()
and
collectionView.scrollRectToVisible()
as well as
collectionView.setContentOffset()
but they all seem to work only after the view has loaded (I tried them via a button in my navigation bar).
Thank you in advance!
EDIT:
Now this works, but I also have another collection view in that one middle cell which holds a list of little 2-paged UICollectionViews which are actually objects from a subclass of UICollectionViewCell called PersonCell each holding a UICollectionView. I want these UICollectionViews to be scrolled to index 1 as well, this is my code:
for tabcell in (collectionView?.visibleCells)! {
if let maincell: MainCell = tabcell as? MainCell {
for cell in maincell.collectionView.visibleCells {
if let c = cell as? PersonCell {
c.collectionView.scrollToItem(at: (NSIndexPath(item: 1, section: 0) as IndexPath), at: [], animated: false)
}
}
}
}
This is executed in the viewDidLayoutSubviews of my 'root' CollectionViewController.
EDIT 2:
Now I tried using following code in the MainCell class (it's a UICollectionViewCell subclass):
func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
let personCell = cell as! PersonCell
personCell.collectionView.scrollToItem(at: (NSIndexPath(item: 1, section: 0) as IndexPath), at: [], animated: false)
}
EDIT 3:
Long story short, I basically need a delegate method that is called after a cell has been added to the UICollectionView.
Did you try [self.collectionView scrollToItemAtIndexPath:indexPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:YES];
Try calling the code in viewDidLayoutSubviews
Okay, I got it!
This SO answer gave me the final hint:
https://stackoverflow.com/a/16071589/3338129
Basically, now I just do this after initialization of the Cell:
self.collectionView.alpha = 1
self.data = data // array is filled with data
self.collectionView.reloadData()
DispatchQueue.main.async {
for cell in self.collectionView.visibleCells {
(cell as! PersonCell).collectionView.scrollToItem(at: (NSIndexPath(item: 1, section: 0) as IndexPath), at: [], animated: false)
}
self.collectionView.alpha = 1
}
Basically, the code in the DispatchQueue.main.async{...} is called on the next UI refresh cycle which means at a point where the cells are already there. To prevent the user from seeing the wrong page for a fraction of a second, I set the whole collectionView's alpha to 0 and toggle it on as soon as the data is there, the cell is there and the page has scrolled.
Related
I'm trying to create hints for new users in iOS application, like to open profile click here, etc. I have a collection view and inside it I have elements that I fetch from server.
I need to show hint near the first element. My code:
var tipView = EasyTipView(
text: "Выбирай предмет и начинай обучение",
preferences: EasyTipView.globalPreferences
)
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let section = sections[indexPath.section]
switch section {
case .fav_subjects:
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "FavSubjectsCollectionViewCell", for: indexPath) as! FavSubjectsCollectionViewCell
let favSubjects = model[.fav_subjects] as! [Subjects.FavSubject]
let cellModel = favSubjects[indexPath.item]
cell.configure(with: cellModel)
//here I'm trying to render hint near first element of collectionView
if indexPath.section == 0 && indexPath.item == 0 {
let view = cell.contentView
tipView.show(forView: view)
}
return cell
case .all_subjects:
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "AllSubjectsCollectionViewCell", for: indexPath) as! AllSubjectsCollectionViewCell
let allSubjects = model[.all_subjects] as! [Subjects.Subject]
let cellModel = allSubjects[indexPath.item]
cell.configure(with: cellModel)
return cell
}
}
}
My problem is when I open screen for the first time my hint displays on the top of the screen and not near the first element, but when I switch to another screen and then go back, hint displays exactly where expected.
I suggest that my problem is screen rendered for the first time before all items fetched from server so tried to use layoutIfNeeded() to rerender when the size is changed but it doesn't help:
tipView.layoutIfNeeded()
if indexPath.section == 0 && indexPath.item == 0 {
let view = cell.contentView
self.tipView.layoutIfNeeded()
self.tipView.show(forView: view)
}
Also I have tried to use viewDidAppear, because I thought that if screen is already rendered than I will have element rendered and I will show hint in the right place for the first render but it turns out that in viewDidAppear cell is nil:
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
let cell = collectionView.cellForItem(at: IndexPath(item: 0, section: 0))
}
Incorrect(when screen opened first time):
Correct:
I'm new to iOS so I think I missed something important, please help.
The method cellForItem(at:) gets called before the cells gets displayed on screen. In fact, at this point the final frame of the cell is not yet determined, it will happen later when the cell gets added to the view hierarchy and the layout pass happens.
In some cases even if cellForItem(at:) gets called, the cell may never appear on screen.
If you always display the hint near the first element, perhaps it will be easier to use the collection view's frame as reference instead of the first cell unless you need the hint to scroll along with the cell.
Alternatively, add the hint as a subview to the cell's contentView and use Auto Layout to define its position inside the cell. Don't forget to remove the hint from the view hierarchy when appropriate because the same cell may end up being dequeued for another index path during scroll.
What I'm trying to do is when I tap the button in a cell, that button in that cell becomes invisible. The problem is when I tap the button, it becomes invisible, but when I scroll the collection view the hidden button goes from one to the other. For example, I tap the second one it hides but when I scroll I see that the 7th becomes hidden. Every time I scroll the hidden button change.
This is the code I wrote:
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell : CollectionViewCellKharid3 = collectionView.dequeueReusableCell(withReuseIdentifier: "customcell3", for: indexPath) as! CollectionViewCellKharid3
cell.lblEsmeMahsul.text = mainCats[indexPath.row]
cell.imgMahsul.af_setImage(withURL: URL(string : (mainadress + "/Opitures/" + mainPicNumbers[indexPath.row]))!, placeholderImage: UIImage(named: "loadings" ))
cell.btnKharid.addTarget(self, action: #selector(btnColectionviewCellTapped), for : UIControlEvents.touchUpInside)
cell.btnKharid.tag = indexPath.row
cell.btnMosbat.addTarget(self, action: #selector(btnMosbatTapped), for : UIControlEvents.touchUpInside)
cell.btnMosbat.tag = indexPath.row
cell.configureCell()
return cell
}
#objc func btnColectionviewCellTapped(_ sender:UIButton){
// let indexPath : IndexPath = self.collectionview1.ind
print(sender.tag)
sender.isHidden = true
}
#objc func btnMosbatTapped(_ sender:UIButton){
let index = IndexPath(item: sender.tag , section: 0)
let cell = self.collectionviewForushVije.cellForItem(at: index) as? CollectionViewCellKharid3
cell?.lblTedad.text = "22"
print(sender.tag)
}
Cells get reused. You need to keep track of which cells have been tapped so you can set the proper button state in your cellForItemAt method.
Declare a property in your class:
var beenTapped: Set<Int> = []
Then in btnColectionviewCellTapped add:
beenTapped.insert(sender.tag)
And in cellForItemAt you need:
cell.btnKharid.isHidden = beenTapped.contains(indexPath.item)
You should also replace the use of indexPath.row with indexPath.item. row is for table views. item is for collection views.
It's a very common mis-use of UICollectionView(or UITableView). When deal with them, you should alway keep one thing in mind, re-use. The collection/tableview cell will be highly reuse by os when on need. The problem cause in your code is, you assume the one time set of one property in a cell will be persistence, which is wrong. The cell come from dequeue method, can always be a new cell or an existing cell, therefore, any configuration should be apply to a cell should be config again. Think in that way, all view in a cell is "dirty" when it get it from collection view, you should set the property you want before return it back(or have a mechanism to set it later). Therefore, in your case, just set the isHidden property every time you prepare the cell in cellForRow delegate.
I have a table view with custom cells. They are quite tall, so only one cell is completely visible on the screen and maybe, depending on the position of that cell, the top 25% of the second one. These cells represent dummy items, which have names. Inside of each cell there is a button. When tapped for the first time, it shows a small UIView inside the cell and adds the item to an array, and being tapped for the second time, hides it and removes the item. The part of adding and removing items works fine, however, there is a problem related to showing and hiding views because of the fact that cells are reused in a UITableView
When I add the view, for example, on the first cell, on the third or fourth cell (after the cell is reused) I can still see that view.
To prevent this I've tried to loop the array of items and check their names against each cell's name label's text. I know that this method is not very efficient (what if there are thousands of them?), but I've tried it anyway.
Here is the simple code for it (checkedItems is the array of items, for which the view should be visible):
if let cell = cell as? ItemTableViewCell {
if cell.itemNameLabel.text != nil {
for item in checkedItems {
if cell.itemNameLabel.text == item.name {
cell.checkedView.isHidden = false
} else {
cell.checkedView.isHidden = true
}
}
}
This code works fine at a first glance, but after digging a bit deeper some issues show up. When I tap on the first cell to show the view, and then I tap on the second one to show the view on it, too, it works fine. However, when I tap, for example, on the first one and the third one, the view on the first cell disappears, but the item is still in the array. I suspect, that the reason is still the fact of cells being reused because, again, cells are quite big in their height so the first cell is not visible when the third one is. I've tried to use the code above inside tableView(_:,cellForRow:) and tableView(_:,willDisplay:,forRowAt:) methods but the result is the same.
So, here is the problem: I need to find an EFFICIENT way to check cells and show the view ONLY inside of those which items are in the checkedItems array.
EDITED
Here is how the cell looks with and without the view (the purple circle is the button, and the view is the orange one)
And here is the code for the button:
protocol ItemTableViewCellDelegate: class {
func cellCheckButtonDidTapped(cell: ExampleTableViewCell)
}
Inside the cell:
#IBAction func checkButtonTapped(_ sender: UIButton) {
delegate?.cellCheckButtonDidTapped(cell: self)
}
Inside the view controller (NOTE: the code here just shows and hides the view. The purpose of the code is to show how the button interacts with the table view):
extension ItemCellsTableViewController: ItemTableViewCellDelegate {
func cellCheckButtonDidTapped(cell: ItemTableViewCell) {
UIView.transition(with: cell.checkedView, duration: 0.1, options: .transitionCrossDissolve, animations: {
cell.checkedView.isHidden = !cell.checkedView.isHidden
}, completion: nil)
}
EDITED 2
Here is the full code of tableView(_ cellForRowAt:) method (I've deleted the looping part from the question to make it clear what was the method initially doing). The item property on the cell just sets the name of the item (itemNameLabel's text).
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
if let cell = tableView.dequeueReusableCell(withIdentifier:
ItemTableViewCell.identifier, for: indexPath) as? ItemTableViewCell{
cell.item = items[indexPath.row]
cell.delegate = self
cell.selectionStyle = .none
return cell
}
return UITableViewCell()
}
I've tried the solution, suggested here, but this doesn't work for me.
If you have faced with such a problem and know how to solve it, I would appreciate your help and suggestions very much.
Try this.
Define Globally : var arrIndexPaths = NSMutableArray()
func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 30
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell:TableViewCell = self.tblVW.dequeueReusableCell(withIdentifier: "TableViewCell", for: indexPath) as! TableViewCell
cell.textLabel?.text = String.init(format: "Row %d", indexPath.row)
cell.btn.tag = indexPath.row
cell.btn.addTarget(self, action: #selector(btnTapped), for: .touchUpInside)
if arrIndexPaths.contains(indexPath) {
cell.backgroundColor = UIColor.red.withAlphaComponent(0.2)
}
else {
cell.backgroundColor = UIColor.white
}
return cell;
}
#IBAction func btnTapped(_ sender: UIButton) {
let selectedIndexPath = NSIndexPath.init(row: sender.tag, section: 0)
// IF YOU WANT TO SHOW SINGLE SELECTED VIEW AT A TIME THAN TRY THIS
arrIndexPaths.removeAllObjects()
arrIndexPaths.add(selectedIndexPath)
self.tblVW.reloadData()
}
I would keep the state of your individual cells as part of the modeldata that lies behind every cell.
I assume that you have an array of model objects that you use when populating you tableview in tableView(_:,cellForRow:). That model is populated from some backend service that gives you some JSON, which you then map to model objects once the view is loaded the first time.
If you add a property to your model objects indicating whether the cell has been pressed or not, you can use that when you populate your cell.
You should probably create a "wrapper object" containing your original JSON data and then a variable containing the state, lets call it isHidden. You can either use a Bool value or you can use an enum if you're up for it. Here is an example using just a Bool
struct MyWrappedModel {
var yourJSONDataHere: YourModelType
var isHidden = true
init(yourJSONModel: YourModelType) {
self.yourJSONDataHere = yourJSONModel
}
}
In any case, when your cell is tapped (in didSelectRow) you would:
find the right MyWrappedModel object in your array of wrapped modeldata objects based on the indexpath
toggle the isHidden value on that
reload your affected row in the table view with reloadRows(at:with:)
In tableView(_:,cellForRow:) you can now check if isHidden and do some rendering based on that:
...//fetch the modelObject for the current IndexPath
cell.checkedView.isHidden = modelObject.isHidden
Futhermore, know that the method prepareForReuse exists on a UITableViewCell. This method is called when ever a cell is just about to be recycled. That means that you can use that as a last resort to "initialize" your table view cells before they are rendered. So in your case you could hide the checkedView as a default.
If you do this, you no longer have to use an array to keep track of which cells have been tapped. The modeldata it self knows what state it holds and is completely independent of cell positions and recycling.
Hope this helps.
Its getting called in viewDidLoad, after fetching the data used.
After some print debugging it looks like it calls all the appropriate delegeate methods, if no data is changed. If there has been some data changed, cellForItemAt does not get called.
Reloading the whole section works fine. But gives me an unwanted animation. Tried disabling UIView animation before, and enabling after reloading section, but still gives me a little animation.
collectionView.reloadSections(IndexSet(integer: 0))
Here is my current situation, when using reloadData()
The UICollectionViewController is a part of a TabBarController.
I'm using custom UICollectionViewCells. The data is loaded from CoreData.
First time opening the tab, its works fine.
After updating the favorites item in another tab, and returning to this collectionView, its not updated. But if i select another tab, and go back to this one, its updated.
var favorites = [Item]()
override func viewWillAppear(_ animated: Bool) {
collectionView!.register(UINib.init(nibName: reuseIdentifier, bundle: nil), forCellWithReuseIdentifier: reuseIdentifier)
if let flowLayout = collectionView!.collectionViewLayout as? UICollectionViewFlowLayout {
flowLayout.estimatedItemSize = CGSize(width: 1,height: 1)
}
loadFavorites()
}
func loadFavorites() {
do {
print("Load Favorites")
let fetch: NSFetchRequest = Item.fetchRequest()
let predicate = NSPredicate(format: "favorite == %#", NSNumber(value: true))
fetch.predicate = predicate
favorites = try managedObjectContext.fetch(fetch)
if favorites.count > 0 {
print("Favorites count: \(favorites.count)")
notification?.removeFromSuperview()
} else {
showEmptyFavoritesNotification()
}
print("Reload CollectionView")
collectionView!.reloadData(
} catch {
print("Fetching Sections from Core Data failed")
}
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
print("Get number of section, \(favorites.count)")
if favorites.count > 0 {
return favorites.count
} else {
return 0
}
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
print("Get cell")
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! SubMenuCell
let menuItem = favorites[indexPath.row]
cell.title = menuItem.title
cell.subtitle = menuItem.subtitle
return cell
}
Console Print/Log
Starting the app, going to the CollectionView tab where there are no favorites:
Load Favorites
Get number of section, 0
Get number of section, 0
Reload CollectionView
Get number of section, 0
Switching tab, and adding and setting an Item object's favorite to true, then heading back to the CollectionView tab:
Load Favorites
Favorites count: 1
Reload CollectionView
Get number of section, 1
The datamodel has 1 item, reloading CollectonView, cellForRowAtIndex not called?
Selecting another tab, random which, then heading back to the CollectionView tab, without changing any data.
Load Favorites
Favorites count: 1
Reload CollectionView
Get number of section, 1
Get cell
Now my Item shows up in the list. You can see from the Get Cell that cellForItemAt is called aswell. Nothing has changed between these last two loggings, just clicked back/fourth on the tabs one time.
Forgot to mention, but this code IS working fine in the simulator.
On a read device its just not giving me any error, just not showing the cell (or calling the cellForItemAt)
After some more debugging i got an error when the items got reduced (instead of increasing like i've tried above).
UICollectionView received layout attributes for a cell with an index path that does not exist
This led med to iOS 10 bug: UICollectionView received layout attributes for a cell with an index path that does not exist
collectionView!.reloadData()
collectionView!.collectionViewLayout.invalidateLayout()
collectionView!.layoutSubviews()
This solved my problem.
I am using autoresizing cells, but i guess this does not explain why cellForItemAt did not get called.
in my case, my collectionview was in a stackview, i didnt make any constraints, when i added the necessary constraints it worked.
Just check collectionview's constraints.
Ok, maybe I can help someone =)
I do this:
Load data from API
Then after load data call DispatchQueue.main.async like this
DispatchQueue.main.async {
self.pointNews = pointNews
}
In self.pointNews didSet I try to do collectionView.reloadData(), but it work only, if I call DispatchQueue.main.async in didSet
DispatchQueue.main.async {
self.collectionView.reloadData()
}
var paths: [IndexPath] = []
if !data.isEmpty {
for i in 0...salesArray.count - 1 {
paths.append(IndexPath(item: i, section: 0))
}
collectionView.reloadData()
collectionView.reloadItems(at: paths)
}
This is the code helped me, for solving this kind of issue.
Post your code.
One possibility is that you are using `URLSession and trying to tell your collection view to update from the it's delegate method/completion closure, not realizing that that code is run on a background thread and you can't do UI calls from background threads.
I faced the same problem with self resizing cells and above solution works as well but collection view scroll position resets and goes to top. Below solution helps to retain your scroll position.
collectionView.reloadData()
let context = collectionView.collectionViewLayout.invalidationContext(forBoundsChange: collectionView.bounds)
context.contentOffsetAdjustment = CGPoint.zero
collectionView.collectionViewLayout.invalidateLayout(with: context)
collectionView.layoutSubviews()
i was facing also this kind of issue so finally i am able to solved using this line of code
[self.collectionView reloadData];
[self.collectionView reloadItemsAtIndexPaths:#[[NSIndexPath indexPathWithIndex:0]]];
I had the same issue. I was updating the height of the UICollectionView based on the content and reloadData() stops working when you set the height of the collection view to zero. After setting a minimum height. reloadData() was working as expected.
I have a CollectionView issue, I have a video showing the problem detailed below. When I click one cell it moves in a weird manner.
Here is my code:
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
selectedFilter = indexPath.row
if filters[indexPath.row] != "Todo" {
filteredNews = news.filter { $0.category == filters[indexPath.row] }
} else {
filteredNews = news
}
tableView.reloadData()
collectionView.reloadData()
}
My Cell is moving, (Just the last cell, don't know why).
I think it might be related to collectionView.reloadData() But I need to do that for updating the green bar you can see on this Video when I select a Cell.
How can I make it not move? Someone had had a similar problem?
I noticed you reloaded a tableView during collectionView didSelectItemAt. If that tableView is a superView of your collectionView that will be the exact reason why you are having this abnormal behaviour.
If it were not, I can offer 3 solutions:
This library have a view controller subclass that can create the effect you want to show.
Manually create a UIView/UIImageView that is not inside the collectionView but update it's position during the collectionView's didSelectItemAt delegate method to but visually over the cell instead - this would require some calculation, but your collectionView will not need to reload.
You can attempt to only reload the two affected cells using the collectionView's reloadItem(at: IndexPath) method.
Know that when you reload a table/collection view, it will not change the current visible cell. However any content in each cell will be affected.
Finally I Solve it! I removed collectionView.reloadData() and added my code to change colors inside didSelectItemAt changing current selected item and old selected item (I created a Variable to see which one was the old selected item).
If someone interested, here is my code:
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let oldSelectedFilter = selectedFilter
if selectedFilter != indexPath.row {
let oldIndexPath = IndexPath(item: oldSelectedFilter, section: 0)
selectedFilter = indexPath.row
if filters[indexPath.row] != "Todo" {
filteredNews = news.filter { $0.category == filters[indexPath.row] }
} else {
filteredNews = news
}
if let cell = collectionView.cellForItem(at: indexPath) as? FiltersCollectionViewCell {
cell.selectedView.backgroundColor = MainColor
}
if let cell = collectionView.cellForItem(at: oldIndexPath) as? FiltersCollectionViewCell {
cell.selectedView.backgroundColor = UIColor(red:0.31, green:0.33, blue:0.35, alpha:1.0)
}
tableView.reloadData()
}
}